First, I have flown US extensively in the past 24 months (although not out of PHL).

It's not perfect, but it's really not that bad. All my flights have been on impeccably clean planes, service has been friendly and professional, and I have not been delayed (flying mainly LGA-DCA or LGA-BOS, and then connecting from these two locations).

The other option at PHL (and usually the best deal) is Southwest, which has a large number of flights out of PHL.

Personally, I would avoid the drive to EWR which might be OK for the occasional flight to Asia or Europe, but is a bear of a drive, especially during rush hour (remember, there is no easy way to get from Philadelphia to Jersey, even though I-95 and the NJ Turnpike are sometimes so close together you can see one road from the other).

Good luck!